[BLOCK] reimplement handling of barrier request

Reimplement handling of barrier requests.

* Flexible handling to deal with various capabilities of
  target devices.
* Retry support for falling back.
* Tagged queues which don't support ordered tag can do ordered.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 58 insertions, 26 deletions

diff --git a/block/elevator.c b/block/elevator.c
index 85a11cee7d1c..39dcccc82ada 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -304,15 +304,7 @@ void elv_requeue_request(request_queue_t *q, struct request *rq)
 
         rq->flags &= ~REQ_STARTED;
 
-        /*
-         * if this is the flush, requeue the original instead and drop the flush
-         */
-        if (rq->flags & REQ_BAR_FLUSH) {
-                clear_bit(QUEUE_FLAG_FLUSH, &q->queue_flags);
-                rq = rq->end_io_data;
-        }
-
-        __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
+        __elv_add_request(q, rq, ELEVATOR_INSERT_REQUEUE, 0);
 }
 
 static void elv_drain_elevator(request_queue_t *q)
@@ -332,8 +324,19 @@ static void elv_drain_elevator(request_queue_t *q)
 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
                        int plug)
 {
+        struct list_head *pos;
+        unsigned ordseq;
+
+        if (q->ordcolor)
+                rq->flags |= REQ_ORDERED_COLOR;
+
         if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER)) {
                 /*
+                 * toggle ordered color
+                 */
+                q->ordcolor ^= 1;
+
+                /*
                  * barriers implicitly indicate back insertion
                  */
                 if (where == ELEVATOR_INSERT_SORT)
@@ -393,6 +396,30 @@ void __elv_add_request(request_queue_t *q, struct request *rq, int where,
                 q->elevator->ops->elevator_add_req_fn(q, rq);
                 break;
 
+        case ELEVATOR_INSERT_REQUEUE:
+                /*
+                 * If ordered flush isn't in progress, we do front
+                 * insertion; otherwise, requests should be requeued
+                 * in ordseq order.
+                 */
+                rq->flags |= REQ_SOFTBARRIER;
+
+                if (q->ordseq == 0) {
+                        list_add(&rq->queuelist, &q->queue_head);
+                        break;
+                }
+
+                ordseq = blk_ordered_req_seq(rq);
+
+                list_for_each(pos, &q->queue_head) {
+                        struct request *pos_rq = list_entry_rq(pos);
+                        if (ordseq <= blk_ordered_req_seq(pos_rq))
+                                break;
+                }
+
+                list_add_tail(&rq->queuelist, pos);
+                break;
+
         default:
                 printk(KERN_ERR "%s: bad insertion point %d\n",
                        __FUNCTION__, where);
@@ -422,25 +449,16 @@ static inline struct request *__elv_next_request(request_queue_t *q)
 {
         struct request *rq;
 
-        if (unlikely(list_empty(&q->queue_head) &&
-                     !q->elevator->ops->elevator_dispatch_fn(q, 0)))
-                return NULL;
-
-        rq = list_entry_rq(q->queue_head.next);
-
-        /*
-         * if this is a barrier write and the device has to issue a
-         * flush sequence to support it, check how far we are
-         */
-        if (blk_fs_request(rq) && blk_barrier_rq(rq)) {
-                BUG_ON(q->ordered == QUEUE_ORDERED_NONE);
+        while (1) {
+                while (!list_empty(&q->queue_head)) {
+                        rq = list_entry_rq(q->queue_head.next);
+                        if (blk_do_ordered(q, &rq))
+                                return rq;
+                }
 
-                if (q->ordered == QUEUE_ORDERED_FLUSH &&
-                    !blk_barrier_preflush(rq))
-                        rq = blk_start_pre_flush(q, rq);
+                if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
+                        return NULL;
         }
-
-        return rq;
 }
 
 struct request *elv_next_request(request_queue_t *q)
@@ -593,7 +611,21 @@ void elv_completed_request(request_queue_t *q, struct request *rq)
          * request is released from the driver, io must be done
          */
         if (blk_account_rq(rq)) {
+                struct request *first_rq = list_entry_rq(q->queue_head.next);
+
                 q->in_flight--;
+
+                /*
+                 * Check if the queue is waiting for fs requests to be
+                 * drained for flush sequence.
+                 */
+                if (q->ordseq && q->in_flight == 0 &&
+                    blk_ordered_cur_seq(q) == QUEUE_ORDSEQ_DRAIN &&
+                    blk_ordered_req_seq(first_rq) > QUEUE_ORDSEQ_DRAIN) {
+                        blk_ordered_complete_seq(q, QUEUE_ORDSEQ_DRAIN, 0);
+                        q->request_fn(q);
+                }
+
                 if (blk_sorted_rq(rq) && e->ops->elevator_completed_req_fn)
                         e->ops->elevator_completed_req_fn(q, rq);
         }